1. Field of the Invention
This invention relates to fuel-injected engines and, in particular, to in-tank, high pressure, fuel pump assemblies for use with such engines.
2. Description of the Prior Art
In a fuel-injected engine, fuel is supplied at a relatively high pressure to one or more injectors which are connected directly to the engine cylinders or to an intake manifold leading to the cylinders. In the prior art, two electrically driven pumps have typically been used to deliver fuel to the injectors: a low pressure pump either near or in the vehicle's fuel tank and a high pressure pump connected to the injectors. For vehicles having two fuel tanks, e.g., medium duty and larger trucks, off-road vehicles, and the like, an additional low pressure pump has been used for the second tank.
In order to reduce the complexity and cost, including the cost of assembly, of such systems, efforts have been made to eliminate the low pressure pump by placing the high pressure pump directly in the vehicle's fuel tank. The primary problems raised by this approach have been in the area of insuring that there is a constant supply of fuel at the intake to the high pressure pump. Specifically, the problem has been to supply the high pressure pump with fuel under low fuel conditions and during times when the vehicle is navigating a sharp turn, traveling over a steep incline, or after the vehicle has been parked on an incline for an extended period of time.
Various approaches have been tried to solve the foregoing problems. For example, the high pressure pump has been housed in a reservoir within the vehicle's fuel tank and fuel has been routed to the reservoir to try to keep it filled. Specifically, the fuel returning from the engine has been routed to the reservoir, and, in some cases, the returning fuel has been used to power a jet pump to bring fuel into the reservoir from the main tank by means of Bernoulli forces.
To date, these approaches, rather than solving the problem, have raised problems of their own. In particular, filling the reservoir with fuel returning from the engine and then recycling that fuel back to the engine through the high pressure pump has been found to result in a "hot fuel" problem wherein the fuel is heated by the hot engine on each pass through the system and eventually reaches a temperature at which it can no longer be properly injected into the engine by the fuel-injection system.
As to using the returning fuel to power a jet pump, this approach has been found to be unsuccessful under conditions of high fuel consumption by the engine. Specifically, when the engine is using more fuel, less fuel is returned to the jet pump and thus less fuel is pulled into the reservoir by the jet pump. Accordingly, with time, the amount of fuel in the reservoir decreases, the temperature of the fuel supplied to the engine rises, and the overall performance of the engine and the fuel-injection system declines. Although theoretically it would be possible to solve this problem by using an oversized high pressure pump capable of supplying sufficient fuel to handle high fuel consumption conditions and still provide sufficient flow through the jet pump, the use of such a pump defeats the purpose of the change from the original two pump approach, namely, to reduce the overall cost of the system.
The present invention, as described in detail below, overcomes these problems by providing an in-tank, high pressure, fuel pump assembly which has minimal hot fuel problems and which entrains essentially a constant amount of fuel into its reservoir irrespective of the amount of fuel consumed by the vehicle's engine.